Network Working Group A. Niemi
Internet-Draft Nokia
Intended status: Standards Track M. Garcia-Martin
Expires: April 8, 2010 Ericsson
G. Sandbakken, Ed.
TANDBERG
October 5, 2009
Multi-party Chat Using the Message Session Relay Protocol (MSRP)
draft-ietf-simple-chat-05
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Copyright (c) 2009 IETF Trust and the persons identified as the
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Abstract
The Message Session Relay Protocol (MSRP) defines a mechanism for
sending instant messages within a peer-to-peer session, negotiated
using the Session Initiation Protocol (SIP) and the Session
Description Protocol (SDP). This document defines the necessary
tools for establishing multi-party chat sessions, or chat rooms,
using MSRP.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivations and Requirements . . . . . . . . . . . . . . . . . 5
4. Overview of Operation . . . . . . . . . . . . . . . . . . . . 7
5. Creating, Joining, and Deleting a Chat Room . . . . . . . . . 10
5.1. Creating a Chat Room . . . . . . . . . . . . . . . . . . . 10
5.2. Joining a Chat Room . . . . . . . . . . . . . . . . . . . 10
5.3. Deleting a Chat Room . . . . . . . . . . . . . . . . . . . 11
6. Sending and Receiving Instant Messages . . . . . . . . . . . . 11
6.1. Regular Messages . . . . . . . . . . . . . . . . . . . . . 11
6.2. Private Messages . . . . . . . . . . . . . . . . . . . . . 12
6.3. MSRP reports and responses . . . . . . . . . . . . . . . . 13
7. Nicknames . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Using Nicknames within a Conference . . . . . . . . . . . 15
7.2. Modifying a Nickname . . . . . . . . . . . . . . . . . . . 16
7.3. Removing a Nickname . . . . . . . . . . . . . . . . . . . 16
7.4. Nicknames in the Conference Event Package . . . . . . . . 16
7.5. Nicknames not supported nor allowed . . . . . . . . . . . 17
8. The SDP 'chatroom' attribute . . . . . . . . . . . . . . . . . 17
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Joining a chat room . . . . . . . . . . . . . . . . . . . 18
9.2. Setting up a nickname . . . . . . . . . . . . . . . . . . 20
9.3. Sending a regular message to the chat room . . . . . . . . 22
9.4. Sending a private message to a participant . . . . . . . . 23
9.5. Chuncked private message . . . . . . . . . . . . . . . . . 25
9.6. Sending a private message using anonymous URI . . . . . . 26
9.7. Nickname in a conference information document . . . . . . 27
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
10.1. New MSRP Method . . . . . . . . . . . . . . . . . . . . . 28
10.2. New MSRP Header . . . . . . . . . . . . . . . . . . . . . 29
10.3. New MSRP Status Codes . . . . . . . . . . . . . . . . . . 29
10.4. New SDP Attribute . . . . . . . . . . . . . . . . . . . . 29
11. Security Considerations . . . . . . . . . . . . . . . . . . . 29
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 30
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 30
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
14.1. Normative References . . . . . . . . . . . . . . . . . . . 30
14.2. Informative References . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
The Message Session Relay Protocol (MSRP) [RFC4975] defines a
mechanism for sending a series of instant messages within a session.
The Session Initiation Protocol (SIP) [RFC3261] in combination with
the Session Description Protocol (SDP) [RFC3264] allows for two peers
to establish and manage such sessions.
In another application of SIP, a user agent can join in a multi-party
conversation called a conference that is hosted by a specialized user
agent called a focus [RFC4353]. Such a conference can naturally
involve MSRP sessions. It is the responsibility of an entity
handling the media to relay instant messages received from one
participant to the rest of the participants in the conference.
Several such systems already exist in the Internet. Participants in
a chat room can be identified with a pseudonym or nickname, and
decide whether their real identity is disclosed to other
participants. Participants can also use a rich set of features such
as the ability to send private instant messages to other
participants.
Similar conferences supporting chat rooms are already available
today. For example, Internet Relay Chat (IRC) [RFC2810], Extensible
Messaging and Presence Protocol [RFC3920] based chat rooms, and many
other proprietary systems provide chat room functionality.
Specifying equivalent functionality for MSRP-based systems provides
competitive features and enables interworking between the systems.
This document defines requirements, conventions, and extensions for
providing private messages and nickname management in centralized
conferences with MSRP. Participants in a chat room can be identified
by a pseudonym, and decide if their real identity is disclosed to
other participants. This memo uses the SIP Conferencing Framework
[RFC4353] as a design basis. It also aims to be compatible with the
A Framework for Centralized Conferencing [RFC5239]. It is expected
that future mechanisms will be developed for providing similar
functionality in generic conferences, i.e., where the media is not
only restricted to MSRP. The mechanisms described in this document
provide a future compatible short-term solution for MSRP centralized
conferences.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119, BCP 14
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[RFC2119], and indicate requirement levels for compliant
implementations.
This memo deals with tightly coupled SIP conferences defined in SIP
Conferencing Framework [RFC4353] adopting the terminology. In
addition to that terminology, we introduce some new terms:
Nickname: a pseudonym or descriptive name associated to a
participant. See Section 7 for details
Multi-party chat: an instance of a tightly coupled conference, in
which the media exchanged between the participants consist of MSRP
based instant messages. Also known as a chat room.
Chat Room: a synonym for a multi-party chat
Chat Room URI: a URI that identifies a particular chat room, and is
a synonym of a Conference URI defined in [RFC4353]
Sender: the conference participant that originally created an
instant message and sent it to the chat room for delivery.
Recipient: the destination conference participant(s). This
defaults to the full conference participant list, minus the IM
Sender.
MSRP switch: a media level entity that is a MSRP endpoint. It is a
special MSRP endpoint that receives MSRP messages, and delivers
them to the other conference participants. The MSRP switch has a
similar role to a conference mixer with the exception that the
MSRP switch does not actually "mix" together different input media
streams; it merely relays the messages between participants.
Private Instant Message: an instant message sent in a chat room
intended for a single participant. A private IM is usually
rendered distinctly from the rest of the IMs, indicating that the
message was a private communication.
Anonymous URI: a temporary Globally Routable User Agent URI (GRUU)
[I-D.ietf-sip-gruu] that can be registered with the conference
focus to conceal a participant's SIP AOR from the other
participants in the conference.
3. Motivations and Requirements
Although conference frameworks describing many types of conferencing
applications already exist, such as the Framework for Centralized
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Conferencing [RFC5239] and the SIP Conferencing Framework [RFC4353],
the exact details of session-based instant messaging conferences are
not well-defined at the moment.
To allow interoperable chat implementations, for both conference-
aware, and conference-unaware user agents, certain conventions for
MSRP conferences need to be defined. It also seems beneficial to
provide a set of features that enhance the baseline multi-party MSRP
in order to be able to create systems that have functionality on par
with existing chat systems, as well as enable building interworking
gateways to these existing chat systems.
We define the following requirements:
REQ-1: A basic requirement is the existence of a multi-party
conference, where participants can join and leave the
conference and get instant messages exchanged to the rest of
the participants.
REQ-2: A conference participant must be able to determine the
identities of the sender and recipient of the received IMs.
REQ-3: A conference participant must be able to determine the
recipient of the received message. For instance, the
recipient of the message might be the entire conference or a
single participant of the conference (i.e., a private
message).
REQ-4: It must be possible to send a message to a single participant
within the conference (i.e., a private instant message).
REQ-5: A conference participant may have a nickname or pseudonym
associated with their real identity.
REQ-6: It must be possible for a participant to change their
nickname during the progress of the conference.
REQ-7: It must be possible that a participant is only known by an
anonymous identity and not their real identity to the rest of
the conference.
REQ-8: It must be possible for the MSRP switch originate IMs to the
conference by owner or administrator (e.g. message of the
day, welcome messages, server is shutting down, etc.)
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REQ-9: It must be possible for the conference participants to learn
the chat room capabilities described in this document.
4. Overview of Operation
In order to set up a conference, one must first be created. Users
wishing to host a conference themselves can of course do just that;
their User Agent (UA) simply morphs from an ordinary UA into a
special purpose one called a Focus UA. Another, commonly used setup
is one where a dedicated node in the network functions as a Focus UA.
Each chat room has an identity of its own: a SIP URI that
participants use to join the conference, e.g. by sending an INVITE
request. The conference focus processes the invitations, and as
such, maintains SIP dialogs with each participant. In an multi-party
chat, or chat room, MSRP is one of the established media streams.
Each conference participant establishes an MSRP session with the MSRP
switch, which is a special purpose MSRP application. The MSRP
sessions can be relayed by one or more MSRP relays found in
[RFC4976]. This is illustrated in Figure 1
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MSRP Sessions
+---------------------------+
| +-----------+ |
+---+--+ +---+--+ | |
| SIP | | SIP | | |
| MSRP | | MSRP | +--+---+----+
|Client| |Client| | MSRP |
+---+--+ ++-----+ | Relay |
| | +-----+-----+
SIP Dialogs | / |
| | | MSRP Sessions
+----+------+--+ |
| Conference | +-------+-----+
| Focus UA | | MSRP |
| |........| Switch |
| | | |
+---+--------+-+ +-------+-----+
| \ |
SIP Dialogs | | | MSRP Sessions
| \ |
+--+---+ +-+----+ +-----+------+
| SIP | | SIP | | MSRP |
| MSRP | | MSRP | | Relay |
|Client| |Client| +-+-------+--+
+---+--+ +--+---+ | |
| +-----------+ |
+------------------------------+
MSRP sessions
Figure 1: Multi-party chat overview shown with MSRP Relays and a
conference Focus UA
The MSRP switch is similar to a conference mixer in that it handles
media sessions with each of the participants and bridges these
streams together. However, unlike a conference mixer, the MSRP
switch merely forwards messages between participants but doesn't
actually mix the streams in any way. The system is illustrated in
Figure 2.
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+------+
| MSRP |
|Client|
+------+ +--.---+ +------+
| MSRP | | | MSRP |
|Client| | _|Client|
+------._ | ,' +------+
`._ | ,'
`.. +----------+ ,'
`| |'
| MSRP |
| Switch |
,| |_
_,-'' +----------+ ``-._
+------.-' | `--+------+
| MSRP | | | MSRP |
|Client| | |Client|
+------+ | +------+
+---'--+
| MSRP |
|Client|
+------+
Figure 2: Multi-party chat in a Centralized Conference
Typically conference participants also subscribe to the conference
event package [RFC4575] to gather information about the conference
roster in the form of conference state notifications. For example,
participants can learn about other participants' identities.
All messages in the chat room use the 'Message/CPIM' wrapper content
type [RFC3862], so that it is possible to distinguish between private
and regular messages. When a participant wants to send an instant
message to the conference, it constructs an MSRP SEND request and
submits it to the MSRP switch including a regular payload (e.g. a
Message/CPIM message that contains a text, html, an image, etc.).
The Message/CPIM To header is set to the chat room URI. The switch
then fans out the SEND request to all of the other participants using
their existing MSRP sessions.
A participant can also send a private instant message addressed to a
participants whose identity has been learned, e.g. via a notification
from the conference event package [RFC4575]. In this case the sender
creates an MSRP SEND request with a Message/CPIM body whose To header
contains not the chat room URI but the recipient's URI. The MSRP
switch then forwards the SEND request to the recipient.
We extend the current MSRP negotiation that takes place in SDP
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[RFC4566] to allow participants to learn whether the chat room
supports and is willing to accept (e.g. due to local policy
restrictions) certain MSRP functions defined in this memo, such as
nicknames or private messaging.
Naturally, when a participant wishes to leave a chat room, it sends a
SIP BYE request to the Focus UA and terminates the SIP dialog with
the focus and MSRP sessions with the MSRP switch.
5. Creating, Joining, and Deleting a Chat Room
5.1. Creating a Chat Room
Since we consider a chat room a particular type of conference having
MSRP media, the methods defined by the SIP Conference Framework
[RFC4353] for creating conferences are directly applicable to a chat
room.
Once a chat room is created, it is identified by a SIP URI, like any
other conference.
5.2. Joining a Chat Room
Participants usually join the conference by sending an INVITE request
to the conference URI. As long as the conference policy allows, the
INVITE request is accepted by the focus and the user is brought into
the conference. Conference aware participants will detect that the
peer is a focus due to the presence of the "isfocus" feature tag
[RFC3840] in the Contact header field of the 200-class response to
the INVITE request. Conference unaware participants will not notice
it is a foucs, and can not apply the additional mechanisms defined in
this document. Participants are also aware that the mixer is an MSRP
switch due to the presence of an 'message' media type and either TCP/
MSRP or TCP/TLS/MSRP as the protocol field in the SDP [RFC4566]
media-line.
The conference focus of a chat room MUST include support for a
Message/CPIM [RFC3862] top-level wrapper for the MSRP messages by
setting the 'accept-types' MSRP media line attribute in the SDP offer
or answer to include 'Message/CPIM'.
Note that the 'Message/CPIM' wrapper is used to carry the sender
information that, otherwise, it will not be available to the
recipient. Additionally, 'Message/CPIM' wrapper carries the
recipient information (e.g. To and Cc: headers).
If a participant wants to remain anonymous to the rest of the
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participants in the conference, the participant's UA can register or
acquire by other means a temporary GRUU with the conference focus.
The procedure SHOULD follow the recommendation of draft-ietf-sip-gruu
[I-D.ietf-sip-gruu]. The temporary GRUU can be used in the From and
To header in the 'Message/CPIM' wrapper concealing the participant's
SIP AOR from the other participants in the conference.
The conference focus of a chat room MUST learn the chat room
capabilities of each participant that joins the chat room, and MUST
inform the MSRP switch of such support. This is to prevent that the
MSRP switch distributes private messages to participants who do not
support private messaging. The recipient could be able to render the
private message, but not supporting private messages the participant
can not respond.
5.3. Deleting a Chat Room
As with creating a conference, the methods defined by the SIP
Conference Framework [RFC4353] for deleting a conference are directly
applicable to a chat room. The MSRP switch will terminate the MSRP
sessions with all the participants.
Deleting a chat room is an action that heavily depends on the policy
of the chat room. The policy can determine that the chat room is
deleted when the creator leaves the conference, or with any out of
band mechanism.
6. Sending and Receiving Instant Messages
6.1. Regular Messages
This section describes the conventions used to send and receive
instant messages that are addressed to all the participants in the
chat room. These are sent over a regular MSRP SEND request that
contains a Message/CPIM wrapper [RFC3862] that in turn contains the
desired payload (e.g. text, image, video-clip, etc.).
When a chat room participant wishes to send an instant message to all
the other participants in the chat room, he constructs an MSRP SEND
request that MUST contain a top-level wrapper of type 'Message/CPIM'
[RFC3862]. The actual instant message payload inside 'Message/CPIM'
MAY be of any type negotiated in the SDP 'accepted-types' attribute
according to the MSRP rules.
The sender SHOULD populate the From header of the Message/CPIM
wrapper with a proper identity by which the user is recognized in the
conference. Identities that can be used (among others) are:
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o A SIP URI [RFC3261] representing the participant's address-of-
record
o A tel URI [RFC3966] representing the participant's telephone
number
o An IM URI [RFC3860] representing the participant's instant
messaging address
o An temporary GRUU [I-D.ietf-sip-gruu] representing the anonymous
URI associated with the sender.
The MSRP switch that receives a SEND request from a participant
SHOULD first verify that the From header field of the Message/CPIM
wrapper is correctly populated with a valid URI.
Then the MSRP switch should inspect the To header field of the
Message/CPIM wrapper. If the To header field of the Message/CPIM
wrapper contains the chat room URI, the MSRP switch can generate a
copy of the SEND request to each of the participants in the
conference except the sender. The MSRP switch MUST NOT modify any of
the bodies included in the received SEND request. Note that the MSRP
switch does not need to wait for the reception of the complete MSRP
chunk or MSRP message before it starts the distribution to the rest
of the participants. Instead, once the MSRP switch has received the
headers of the Message/CPIM body it SHOULD start the distribution
process. Having the Message/CPIM header only in the first chunk, the
MSRP switch MUST track the Message-Id until the last chunk of the
message has been distributed.
An MSRP endpoint that receives a SEND request from the MSRP switch
containing a Message/CPIM wrapper SHOULD first inspect the To header
field of the Message/CPIM body. If the To header field is set to the
chat room URI, it should render it is a regular message that has been
distributed to all the participants in the conference. Then the MSRP
endpoint SHOULD inspect the From header field of the Message/CPIM
body to identify the sender. The From header field will include a
URI that identifies the sender. The endpoint might have also
received further identity information through a subscription to the
SIP conference event package [RFC4575].
6.2. Private Messages
This section describes the conventions used to send and receive
private instant messages, i.e., instant messages that are addressed
to one participant of the chat room rather to all of them. A chat
room can signal support for private messages using the chatroom-
attribute (see Section 8 for details).
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When a chat room participant wishes to send a private instant message
to a participant the chat room, it follows the same procedures for
creating a SEND request as for regular messages (Section 6.1). The
only difference is that the MSRP endpoint MUST populate the To header
of the Message/CPIM with the identity of the intended recipient. The
identity can be SIP, TEL, and IM URIs typically learned from the
information received in notifications of the conference event package
[RFC4575].
As for regular messages, the MSRP switch that receives a SEND request
from a participant SHOULD first verify that the From header field of
the Message/CPIM wrapper is correctly populated with a valid URI, and
that the recipient is supporting private messages. See section
Section 6.3 for report and response handling. If successful, the
MSRP switch should search it's mapping table to find the MSRP session
established towards the recipient. If a match is found the MSRP
switch MUST create a SEND request and MUST copy the contents of the
sender's message to it.
An MSRP endpoint that receives a SEND request from the MSRP switch
does the same validations as for regular messages (Section 6.1). If
the To header field is different from the chat room URI, the MSRP
endpoints know that it is a private message. It should render who it
is from based on the From header of the Message/CPIM wrapper
It is possible that a participant, identified by a SIP Address of
Record, joins a conference of instant messages from two or more
different SIP UAs. It is RECOMMENDED that the the MSRP switch can
map a participant or anonymous URI for two or more MSRP sessions. If
the policy of the server allows for this, the MSRP switch MUST copy
all messages intended for the recipient through each MSRP session.
6.3. MSRP reports and responses
The MSRP SHALL follow the success report and failure report handling
described in section 7 of [RFC4975]. For regular messages the MSRP
switch MUST act as a MSRP endpoint receiver of the request according
to section 5.3 of [RFC4975].
For regular messages the MSRP switch MAY use any report model in the
copies of the regular SEND request intended for the recipients, but
any received reports MUST NOT be forwarded to the originator of the
original SEND request. This could lead to having the sender
receiving multiple reports for a single MSRP request. The MSRP
switch for regular messages SHALL construct responses according to
section 7.2 of [RFC4975]. If the URI included in the From header
field of the Message/CPIM wrapper is not valid (e.g, because it does
not "belong" to the user), the response code is 403. Otherwise the
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response code is 200.
Private messages (section Section 6.2) handle MSRP reports
differently from regular chat room messages. The MSRP switch acts
transparently having an end-to-end relationship between the sender
and the recipient. The MSRP switch MUST for private messages keep
any Sucess-Report and Failure-Report headers in the relayed request.
Any reports or responses from the recipient MUST be forwarded to the
sender.
For private messages the MSRP switch MUST follow section 7.2 of
[RFC4975] in the following error scenarios. The MSRP switch MUST
inspect the To header field of the Message/CPIM wrapper. If the To
header field of the Message/CPIM wrapper in the request does not
contain the chat room URI, it must check if it contains a
participants URI associated with a participant. If the URI in the To
header can not be resolved (e.g. cased by a mistyped URI or that the
recipient has abandoned he chat room), the response error code is
427. The new 427 status code indicates a failure to resolve the
recipient URI in the To header field. If the recipient doesn't
support private messages, the response code is 428. The new response
428 indicate that the recipient does not support private messages. A
REPORT request MUST include a Message/CPIM wrapper, with the original
From header field included in the SEND request, and the To header
field of the original message. The message MUST NOT be forwarded to
the recipient if above conditions applies.
7. Nicknames
A common characteristic of existing chat room services is that
participants have the ability to present themselves with a nickname
to the rest of the participants of the conference. It is used for
easy reference of participants in the chat room, and can also provide
anonymous participants with a meaningful descriptive name.
A nickname is a useful construct in many use cases, of which MSRP
chat is but one example. It is associated with a URI of which the
participant is known to the focus. It is a user selectable
appearance of which the participant wants to be known to the other
participants. It is not a 'display-name', but it is used somewhat
like a display name. A main difference is that a nickname is unique
inside a chat room to allow an unambiguous reference to a participant
in the chat. Nicknames may be long lived, or may be temporary.
Users also need to reserve a nickname prior to its utilization.
This memo specifies the nickname as a string. The nickname string
MUST be unambiguous within the scope of the chat room (conference
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instance). This scope is similar to having a nickname unique inside
a chat room from Extensible Messaging and Presence Protocol
[RFC3920]. The chat room may have policies associated with
nicknames. It may not accept nickname strings at all, or a it may
provide a wider unambiguous scope like a domain or server, similar to
Internet Relay Chat (IRC) [RFC2810].
7.1. Using Nicknames within a Conference
This memo provides a mechanism to reserve a nickname for a
participant for as long as the participant is logged into the chat
room. The mechanism is based on a NICKNAME MSRP method (see below)
and a new "Use-Nickname" header. Note that other mechanisms may
exist (for example, a web page reservation system), although they are
outside the scope of this document.
A conference participant who has established an MSRP session with the
MSRP switch, where the MSRP switch has indicated the support and
availability of nicknames with the 'nicknames' token in the
'chatroom' SDP attribute, MAY send a NICKNAME request to the MSRP
switch. The NICKNAME request MUST include a new Use-Nickname header
that contains the nickname string that the participant wants to
reserve.
The MSRP switch that receives a NICKNAME request containing a
nickname in the Use-Nickname header field SHOULD first verify whether
the policy of the chat room allows the nickname functionality. If is
not allowed, the MSRP the response code is 501 section 7.2 of
[RFC4975] for constructing a response.
If the policy of the chat room allows the usage of nicknames, the
MSRP switch SHOULD validate that the SIP AOR is entitled to reserve
the nickname. The participant's authenticated identity can be
derived after a successful HTTP Digest Authentication, included in a
trusted SIP P-Asserted-Identity header field, included in a valid SIP
Identity header field, or derived from any other present or future
SIP authentication mechanism. Once the MSRP switch has validated
that the participant is entitled to reserve the nickname, the
response code is 200.
The reservation of a nickname can fail, e.g. if the NICKNAME request
contains a malformed or non-existent Use-Nickname header field, or if
the same nickname has already been reserved by another participant in
the conference. The validation can also fail where the SIP AOR is
not entitled to reserve the nickname. In any of these cases the MSRP
response code is 423.The semantics of the 423 response are: "Nickname
usage failed; the nickname is not allocated to this user".
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As indicated earlier, this specification defines a new MSRP header
field: "Use-Nickname". The Use-Nickname header field carries a
nickname string, and SHOULD be included in the NICKNAME requests.
The syntax of the NICKNAME method and the "Use-Nickname" header field
is built upon the MSRP formal syntax [RFC4975]
ext-method =/ NICKNAMEm
NICKNAMEm = %x4E.49.43.4B.4E.41.4D.45 ; NICKNAME in caps
ext-header =/ Use-Nickname
; ext-header is specified in RFC 4975
Use-Nickname = "Use-Nickname" ":" nickname
nickname = quoted-string
7.2. Modifying a Nickname
Typically participants will reserve a nickname as soon as they join
the chat room. But it is also possible for participants to modify
their own nicknames and replace them it a new one at any time during
the duration of the MSRP session. Modification of the nickname is
not different from the initial reservation and usage of a nickname,
thus the NICKNAME method is used as described in Section 7.1.
If a NICKNAME request that attempts to modify the current nickname of
the user for some reason fails, the current nickname stays in effect.
A new nickname comes into effect and the old one is released only
after a NICKNAME request is accepted with a 200 response.
7.3. Removing a Nickname
If the participant no longer wants to be known by a nickname in the
conference, the participant can follow the method described in
Section 7.2. The nickname element of the Use-Nickname header MUST be
set to an empty quoted string.
7.4. Nicknames in the Conference Event Package
Typically the conference focus acts as a notifier of the SIP
conference event package [RFC4575]. The conference focus MAY notify
subscribers of the nickname reserved by a given participant. We
define an extension to the conference event package to include
nicknames. The extension adds a child element to the
element containing the nickname string.
The following element is to be added to the sequence of the USER-TYPE
in the XML schema in conference event package [RFC4575]
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7.5. Nicknames not supported nor allowed
The participants of the conference are identified by the SIP, TEL and
IM URI's typically learned from the information received in
notifications of the conference event package [RFC4575]. If
nicknames are not supported nor allowed, the participant list of the
conference will be less presentable.
8. The SDP 'chatroom' attribute
There are a handful of use cases where a participant would like to
learn the chat room capabilities supported by the MSRP switch and the
chat room. For example, a participant would like to learn if the
MSRP switch supports private messaging, otherwise, the participant
may send what he believes is a private instant message addressed to a
participant, but since the MSRP switch does not support the functions
specified in this memo, the message gets eventually distributed to
all the participants of the chat room.
The reverse case also exists. A participant, say Alice, whose user
agent does not support the extensions defined by this document joins
the chat room. The MSRP switch learns that Alice application does
not support private messaging nor nicknames. If another participant,
say Bob, sends a private message to Alice, the MSRP switch does not
distribute it to Alice, because Alice is not able to differentiate it
from a regular message sent to the whole roster. Further more, if
Alice replied to this message, she would do it to the whole roster.
Because of this, the MSRP switch keeps also track of users who do not
support the extensions defined in this document.
In another scenario, the policy of a chat room may indicate that
certain functions are not allowed. For example, the policy may
indicate that nicknames or private messages are not allowed.
In order to provide the user with a good chat room experience, we
define a new 'chatroom' SDP attribute. The 'chatroom' attribute is a
media-level attribute that MAY be included in conjunction with and
MSRP media stream (i.e., when an m= line in SDP indicates "TCP/MSRP"
or "TCP/TLS/MSRP"). The 'chatroom' attribute indicates the
intersection of support and chat room local policy allowance for a
number of functions specified in this document. Specifically, we
provide the means for indicating support to use nicknames and private
messaging.
The 'chatroom' SDP attribute has the following syntax:
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chatroom = chatroom-label ":" chat-token *(SP chat-token)
chatroom-label = "chatroom"
chat-token = (nicknames-token | private-msg-token | token)
nicknames-token = "nicknames"
private-msg-token = "private-messages"
A conference focus that includes the 'nicknames' token in the session
description is signaling that the MSRP switch supports and the chat
room allows to use of the procedures specified in Section 7. A
conference focus that includes the 'private-messages' in the SDP
description is signaling that the MSRP switch supports and the chat
room allows to use of the procedures specified in Section 6.2.
Example of the 'chatroom' attribute for an MSRP media stream that
indicates the acceptance of nicknames and private messages:
a=chatroom:nickname private-messages
9. Examples
9.1. Joining a chat room
Figure 3 presents a flow diagram where Alice joins a chat room by
sending an INVITE request. This INVITE request contains a session
description that includes the chatroom extensions defined in this
document.
Alice Conference focus
| |
|(1) (SIP) INVITE |
|----------------------->|
|(2) (SIP) 200 OK |
||
| |
Figure 3: Flow diagram of a user joining a chat room
F1: Alice constructs an SDP description that includes an MSRP media
stream. She also indicates her support for the chatroom extensions
defined in this document. She sends the INVITE request to the chat
room server.
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INVITE sip:chatroom22@chat.example.com SIP/2.0
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
Max-Forwards: 70
From: Alice ;tag=9fxced76sl
To: Chatroom 22
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 INVITE
Contact:
Content-Type: application/sdp
Content-Length: [length]
v=0
o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
s=-
c=IN IP4 atlanta.example.com
m=message 7654 TCP/MSRP *
a=accept-types:message/cpim text/plain text/html
a=path:msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
a=chatroom:nickname private-messages
Figure 4: INVITE request containing an SDP offer with chat room
extensions
F2: The chat room server accepts the session establishment. It
includes the 'isfocus' and other relevant feature tags in the Contact
header field of the response. The chat room server also builds an
SDP answer that also that forces the reception of messages wrapped in
message/cpim envelops. It also includes the the chatroom attribute
with the allowed extensions.
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SIP/2.0 200 OK
Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9
;received=192.0.2.101
From: Alice ;tag=9fxced76sl
To: Chatroom 22 ;tag=8321234356
Call-ID: 3848276298220188511@atlanta.example.com
CSeq: 1 INVITE
Contact: \
;methods="INVITE,BYE,OPTIONS,ACK,CANCEL,SUBSCRIBE,NOTIFY" \
;automata;isfocus;message;event="conference"
Content-Type: application/sdp
Content-Length: [length]
v=0
o=chat 2890844527 2890844527 IN IP4 chat.example.com
s=-
c=IN IP4 chat.example.com
m=message 12763 TCP/MSRP *
a=accept-types:message/cpim
a=accept-wrapped-types:text/plain text/html *
a=path:msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
a=chatroom:nickname private-messages
Figure 5: 200 (OK) response including chat room extensions
F3: The session established is acknowledged (details not shown).
9.2. Setting up a nickname
Figure 6 shows an example of Alice setting up a nickname using the
conference as provider. Her first proposal is not accepted because
the proposed nickname is already in use. Her second proposal is
accepted.
Alice MSRP switch
| |
|(1) (MSRP) NICKNAME |
|----------------------->|
|(2) (MSRP) 423 |
||
|(4) (MSRP) 200 |
|
Internet-Draft Multi-party Chat MSRP October 2009
F1: Alice sends an MSRP NICKNAME request that contains her proposed
nicknames in the Set-Nickname header field.
MSRP d93kswow NICKNAME
To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
Use-Nickname: "Alice the great"
-------d93kswow$
Figure 7: MSRP NICKNAME request with an initial nickname proposal
F2: The MSRP switch analyzes the existing allocation of nicknames and
detects that the nickname "Alice is great" is already provided to
another participant by the conference. The MSRP switch answers with
a 423 response.
MSRP d93kswow 423 Nickname usage failed
To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
-------d93kswow$
Figure 8: MSRP 423 response
F3: Alice receives the response. She proposes a new nickname in a
second NICKNAME request.
MSRP 09swk2d NICKNAME
To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
Use-Nickname: "Alice in wonderland"
-------09swk2d$
Figure 9: MSRP NICKNAME request with a second nickname proposal
F4: The MSRP switch accepts the nickname proposal and answers with a
200 response.
MSRP 09swk2d 200 OK
To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
-------09swk2d$
Figure 10: MSRP NICKNAME request
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9.3. Sending a regular message to the chat room
Figure 11 depicts a flow diagram where Alice is sending a regular
message addressed to the chat room. The MSRP switch distributes the
message to the rest of the participants.
Alice MSRP switch Bob Charlie
| | | |
| (1) (MSRP) SEND | | |
|--------------------->| (3) (MSRP) SEND | |
| (2) (MSRP) 200 |----------------------->| |
||
| | (5) (MSRP) 200 OK | |
| |
From:
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello guys, how are you today?
-------3490visdm$
Figure 12: Instant message addressed to all participants in the chat
room
F2: The MSRP switch acknowledges the reception of the SEND request
with a 200 (OK) response.
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MSRP 3490visdm 200 OK
To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
Message-ID: 99s9s2
Byte-Range: 1-*/*
-------3490visdm$
Figure 13: 200 (OK) response
F3: The MSRP switch creates a new MSRP SEND request that contains the
received message/cpim body and sends it to Bob.
MSRP 490ej23 SEND
To-Path: msrp://client.biloxi.example.com:4923/49dufdje2;tcp
From-Path: msrp://chat.example.com:5678/jofofo3;tcp
Message-ID: 304sse2
Byte-Range: 1-*/*
Content-Type: message/cpim
To:
From:
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello guys, how are you today?
-------490ej23$
Figure 14: Instant message sent to all participants
The rest of the message flows are analogous to the previous. They
are not shown here.
9.4. Sending a private message to a participant
Figure 15 depicts a flow diagram where Alice is sending a private
message addressed to Bob's SIP AOR. The MSRP switch distributes the
message only to Bob.
Alice MSRP switch Bob
| | |
| (1) (MSRP) SEND | |
|--------------------->| (3) (MSRP) SEND |
| (2) (MSRP) 200 |----------------------->|
|
Internet-Draft Multi-party Chat MSRP October 2009
F1: Alice builds a text message and wraps it in a CPIM message. She
addresses the CPIM message to the Bob's nickname, which she learned
from a notification in the conference event package. She encloses
the result in an MSRP SEND request and sends it to the MSRP switch
via the existing TCP connection.
MSRP 6959ssdf SEND
To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
Message-ID: okj3kw
Byte-Range: 1-*/*
Content-Type: message/cpim
To:
From:
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello Bob.
-------6959ssdf$
Figure 16: Private instant message addressed to one participant
F2: The MSRP switch acknowledges the reception of the SEND request
with a 200 (OK) response.
MSRP 6959ssdfm 200 OK
To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
Message-ID: okj3kw
Byte-Range: 1-*/*
-------6959ssdfm$
Figure 17: 200 (OK) response
F3: The MSRP switch creates a new MSRP SEND request that contains the
received message/cpim body and sends it only to Bob. Bob can
distinguish the sender in the From header of the CPIM message. He
also identifies this as a private message due to the To CPIM header.
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MSRP 9v9s2 SEND
To-Path: msrp://client.biloxi.example.com:4923/49dufdje2;tcp
From-Path: msrp://chat.example.com:5678/jofofo3;tcp
Message-ID: d9fghe982
Byte-Range: 1-*/*
Content-Type: message/cpim
To:
From:
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello Bob.
-------9v9s2$
Figure 18: Private instant message sent to Bob
9.5. Chuncked private message
Figure 19 depicts an example of the private message in Section 9.4
split in two chuncks. The MSRP switch must wait for the complete set
of CPIM headers before distributing the messages.
MSRP 7443ruls SEND
To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
Message-ID: aft4to
Byte-Range: 1-*/174
Content-Type: message/cpim
To:
From:
-------7443ruls$
MSRP 7443ruls SEND
To-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
From-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
Message-ID: aft4to
Byte-Range: 68-174/174
Content-Type: message/cpim
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello Bob
-------7443ruls$
Figure 19: Chuncked private message
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9.6. Sending a private message using anonymous URI
Figure 20 depicts a flow diagram where Alice is utilizing the
temporary GRUU when sending a private message to Bob
Alice MSRP switch Bob
| | |
| (1) (MSRP) SEND | |
|--------------------->| (3) (MSRP) SEND |
| (2) (MSRP) 200 |----------------------->|
|
From:
DateTime: 2009-03-02T15:02:31-03:00
Content-Type: text/plain
Hello Bob.
-------7443ruls$
Figure 21: Anonymous private instant message
F2: The MSRP switch inspects the From header field and verifies that
the temp-gruuu in registered to Alice. If the temporary gruu is
valid, the MSRP acknowledges the reception of SEND request with a 200
(OK) response
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MSRP 7443ruls 200 OK
To-Path: msrp://client.atlanta.example.com:7654/jshA7weztas;tcp
From-Path: msrp://chat.example.com:12763/kjhd37s2s20w2a;tcp
Message-ID: aft4to
Byte-Range: 1-*/*
-------7443ruls$
Figure 22: 200 (OK) response
Flow F3 is not shown
9.7. Nickname in a conference information document
Figure 23 depicts two user elements in a conference information
document both having the nickname element with a nickname string.
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MSRP nickname example2BobsterDepressed Donkey
Figure 23: Nickname in a conference information document
10. IANA Considerations
10.1. New MSRP Method
This specification defines a new MSRP method to be added to the
Methods sub-registry under the MSRP Parameter registry: NICKNAME.
See section Section 7 for details.
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10.2. New MSRP Header
This specification defines a new MSRP header to be added to the
header-field sub registry under the MSRP Parameter registry:
Use-Nickname. See section Section 7 for details.
10.3. New MSRP Status Codes
This specification defines three new MSRP status codes to be added to
the Status-Code sub-registry under MSRP parameters.
The 427 status code indicates the failure to resolve the recipient
URI in the To header field of the Message/CPIM wrapper in the SEND
request. See section for details.
The 428 status code indicates that the recipient of a SEND request
does not support private messages. See section for details.
The 423 response indicates that the requested nickname is not
allocated to the user requesting it. See section Section 7 for
details.
10.4. New SDP Attribute
This specification defines a new media level attribute in the Session
Description Protocol (SDP) Parameters registry: chatroom. See
section Section 8 for details.
11. Security Considerations
This document proposes extensions to the Message Session Relay
Protocol [RFC4975]. Therefore, the security considerations of such
document apply to this document as well.
In general, messages sent to a multi-party session based messaging
focus are not deem to expose any security threat. Nevertheless, if a
participant wants to avoid eavesdropping from non authorized
entities, it should send those messages a TLS [RFC5246] transport
connection, as allowed by MSRP.
Nicknames will be used to show the appearances of the participants of
the conference. A successful take over of a nickname from a
participant might lead to private messages to be sent to the wrong
destination. The recipient's URI will be different from the URI
associated to the original owner of the nickname, but the sender
might not notice this. To avoid take overs the MSRP switch MUST make
sure that a nickname is unique inside a chat room. Also the security
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consideration for any authenticated identity mechanisms used to
validate the SIP AOR will apply to this document as well. If a
nickname can be reserved if it previously has been used by another
participant in the chat room, is up to the policy of the chat room.
12. Contributors
This work would have never been possible without the fruitful
discussions in the SIMPLE WG mailing list, specially with Brian Rosen
(Neustar) and Paul Kyzivat (Cisco), who provided extensive review and
improvements throughout the document.
13. Acknowledgments
The authors want to thank Eva Leppanen, Adamu Haruna, Adam Roach,
Matt Lepinski, Mary Barnes and Ben Campbell for providing comments.
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004.
[RFC3860] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.
[RFC3862] Klyne, G. and D. Atkins, "Common Presence and Instant
Messaging (CPIM): Message Format", RFC 3862, August 2004.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC4575] Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
Initiation Protocol (SIP) Event Package for Conference
State", RFC 4575, August 2006.
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[RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007.
[RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
September 2007.
[RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for
Centralized Conferencing", RFC 5239, June 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[I-D.ietf-sip-gruu]
Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-15 (work in progress),
October 2007.
14.2. Informative References
[RFC2810] Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
April 2000.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.
[RFC4353] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353,
February 2006.
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Authors' Addresses
Aki Niemi
Nokia
P.O. Box 407
NOKIA GROUP, FIN 00045
Finland
Phone: +358 50 389 1644
Email: aki.niemi@nokia.com
Miguel A. Garcia-Martin
Ericsson
Calle Via de los Poblados 13
Madrid, ES 28033
Spain
Email: miguel.a.garcia@ericsson.com
Geir A. Sandbakken (editor)
TANDBERG
Philip Pedersens vei 20
N-1366 Lysaker
Norway
Phone: +47 67 125 125
Email: geir.sandbakken@tandberg.com
URI: http://www.tandberg.com
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